1. Field
The present disclosure relates to a parking assist apparatus and a parking assist method and is particularly suitable for use in a parking assist apparatus and a parking assist method in which an image indicating a parking range of a vehicle is displayed in such a manner as to be superimposed on a viewpoint-converted image on the basis of vehicle speed information and steering angle information acquired from the vehicle along with movement of the vehicle.
2. Description of the Related Art
In related art, when a vehicle is reversed into a parking space, a technique has been used where a display in the vehicle displays a vehicle rearward image, which is an image of an area rearward of the vehicle, captured by a rear camera, or a viewpoint-converted image generated from the vehicle rearward image. The viewpoint-converted image is an image of the area rearward of the vehicle as viewed from a virtual viewpoint above the vehicle by subjecting the vehicle rearward image to viewpoint conversion. A driver drives while viewing a positional relationship between a parking frame and the vehicle within the image displayed on the display, thereby enabling the vehicle to be parked in a predetermined parking frame.
However, as the vehicle moves rearward, the range of the parking frame appearing in the vehicle rearward image is gradually narrowed, and finally almost no parking frame appears in the vehicle rearward image. In this case, it is difficult for the driver to check, from the image, whether the vehicle has been properly parked within the parking frame.
FIGS. 8A and 8B each illustrate an example of an existing vehicle-surroundings image. A vehicle-surroundings image 800 illustrated in FIG. 8A is generated from a viewpoint-converted image 820 obtained by subjecting a vehicle rearward image to viewpoint conversion, and an image 810 of a driver's vehicle. In the viewpoint-converted image 820, there appears a parking frame composed of a white line 821 rearward of the vehicle, a white line 822 on the left side of the vehicle, and a white line 823 on the right side of the vehicle. As illustrated in FIG. 8A, when the vehicle is away from the white line 821 rearward of itself, the white lines 822 and 823 on the left and right sides of the vehicle appear in the viewpoint-converted image 820 with their lengths being relatively long. In this case, a driver checks a positional relationship between the image 810 of the driver's vehicle and the white lines 822 and 823 appearing in the viewpoint-converted image 820 via the vehicle-surroundings image 800 and thus can check whether the vehicle has been properly parked within the parking frame.
On the other hand, when the vehicle moves closer to the white line 821, a vehicle-surroundings image 800′ illustrated in FIG. 8B is generated from the viewpoint-converted image 820 obtained by subjecting the vehicle rearward image to viewpoint conversion, and the image 810 of the driver's vehicle. As illustrated in FIG. 8B, when the vehicle moves closer to the white line 821 rearward of itself, almost no white lines 822 and 823 on the left and right sides of the vehicle appear in the viewpoint-converted image 820. In this case, it is difficult for the driver to check, from the vehicle-surroundings image 800′, whether the vehicle has been properly parked within the parking frame.
Thus, in an existing technique in which a viewpoint-converted image is generated from a vehicle rearward image captured by a camera and is displayed, a technique is developed in which a position of a current parking frame is calculated on the basis of a position of a past parking frame detected from a past vehicle rearward image and information on movement of a vehicle, and in which an image of a pseudo-parking frame indicating the calculated position of the current parking frame is combined with a current viewpoint-converted image and is displayed.
For example, Japanese Unexamined Patent Application Publications Nos. 2010-232723 and 2010-184607 each disclose a technique in which a raw image of an area rearward of a vehicle captured by a camera is displayed in a rearward image display region of a display and also in which a computer-graphic vehicle and a white line (pseudo-parking frame image) detected from a past image stored in a memory are drawn at respective corresponding positions in a history display region of the display. In the technique disclosed in Japanese Unexamined Patent Application Publications Nos. 2010-232723 and 2010-184607, in particular, an accurate position of the white line (pseudo-parking frame image) with respect to the vehicle (computer-graphic vehicle) is maintained using signals regarding vehicle movement (a movement distance and a rotation direction) in accordance with movement of the vehicle.
Japanese Unexamined Patent Application Publication No. 2006-160194 discloses a technique in which, even in the case where there is actually no parking guide, such as a white line, when it is determined, from an image obtained by subjecting an image captured by a camera to viewpoint conversion, that there is a parking space in a position adjacent to another vehicle, a pseudo-parking white line image indicating the same number of spaces as the number of vehicles that can be parked in the parking space is drawn on a parking space in the viewpoint-converted image. Furthermore, Japanese Unexamined Patent Application Publication No. 2006-160194 discloses a technique in which a parking white line image is redrawn in accordance with movement (turning action) of a driver's vehicle.
Japanese Unexamined Patent Application Publications Nos. 2010-232723 and 2010-184607 each describe that a movement distance of the vehicle is determined from the number of revolutions of a wheel. A movement distance of a vehicle can be typically determined from vehicle speed information of the vehicle. However, in a typical vehicle, no vehicle speed information can be acquired if the vehicle speed is less than 1 km/h. For this reason, in a method in which a movement distance of a vehicle is calculated on the basis of vehicle speed information, if the vehicle moves at a speed of less than 1 km/h, the vehicle is regarded as being stopped, and thus a movement distance of the vehicle cannot be calculated accurately. As a result, a position in which a pseudo-parking frame is displayed with respect to the vehicle cannot be displayed accurately.
Japanese Unexamined Patent Application Publication No. 2013-55410 discloses a vehicle-surroundings image display control apparatus that causes a display to display, as a vehicle-surroundings image, an image obtained by combining a real image based on a latest captured image with a history image generated using a past captured image on the basis of vehicle movement amount information, and discloses a technique in which, during a time that elapses before subsequent vehicle movement amount information is acquired, an expected movement amount of a vehicle is estimated on the basis of previously acquired vehicle movement amount information. It can be considered that, even if no vehicle speed information can be acquired when the vehicle speed is less than 1 km/h, use of this technique enables an expected movement amount of a vehicle to be estimated on the basis of previously acquired vehicle movement amount information and enables a pseudo-parking frame to be displayed in a position corresponding to the expected movement amount.
However, even when an expected movement amount is calculated in this way and a pseudo-parking frame is displayed in an expected position, there is some question as to how a vehicle moves in actuality, and thus an error in the position in which the pseudo-parking frame is displayed occurs in some cases. In the related art, however, because a pseudo-parking frame is displayed as if it is displayed accurately, when a user believes a display of the pseudo-parking frame to be accurate and moves his or her vehicle, the vehicle cannot be parked in an intended position. In the technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-160194, a parking white line that does not actually exist is drawn, and no movement distance of a vehicle is used. For this reason, even when the technique disclosed in Japanese Unexamined Patent Application Publication No. 2006-160194 is used, such an issue cannot be solved.
To solve such issues, one or more aspects of the present disclosure enable, if there is a possibility of occurrence of an error in the position of a pseudo-parking frame, a user to move a vehicle on the basis of the possibility of the error.